As heat retaining sheets, batting and quilted materials formed by sewing the batting with fabric having conventionally been known. To improve the heat retaining properties of clothes by the use of heat retaining webs, it has been necessary to increase the thickness of the heat retaining sheet or to increase its apparent density at the sacrifice of the drapability and functionality of the clothes when the clothes are worn, resulting in an unattractive appearance of the clothes. Hence, the application of the heat retaining sheet has been limited to clothes for use in cold weather such as ski wear.
To solve this problem, Japanese Patent Laid-Open No. 41577/1978, for example, proposes a web of undrawn micro-fibers formed by melt-blowing polyethylene terephthalate, polyamide or polypropylene. However, the non-woven web consisting of polyethylene terephthalate exhibits large area shrinkage in boiling water, generally scoring a value of at least 60%. When the heat retaining material is worn for an extended period or is washed repeatedly, problems such as creasing and breakage of yarns are likely to occur due to the difference in shrinkage between the web and various woven or knitted fabrics attached to the surface thereof. In the case of the non-woven web of fibers consisting of polyamide, recovery of compressive elasticity is generally 50% or less and bending rigidity is poor. In addition, it has poor washability because shrinkage during washing is as large as 10%. On the other hand, non-woven fabric consisting of a low heat-resistant polymer such as polypropylene undergoes shrinkage or is fused with the resulting lowered elastic recovery when subjected to various operations for clothes, such as pressing. If exposed to a high temperature environment for an extended period, for example, at 150.degree. C. for 1.5 hour, the web suffers from a critical drawback in that autogenous ignition occurs.
On the other hand, as an attempt to impart stretchability to the non-woven web, it has been known to employ an elastic adhesive or fiber.
When an elastic adhesive is used, however, adhesion between the web and the adhesive is not sufficient and surface destruction occurs when the web is stressed. Also a sufficient stretch recovery properties can not be obtained.
As a method for using elastic fibers, Japanese Patent Laid-Open No. 16910/1980 discloses a method wherein an elastic film containing a foaming agent is expanded and then stretched to obtain a web having a reticular non-woven structure. Since, however, the fiber structure of this reticular web is formed by stretching after expansion, the fiber structure is strongly bundled in the stretching direction and since the size of the fibers is great and the fibers are not sufficiently separated and independent, flexibility is insufficient.